Method of machining globoidal worm gears



March 26, 1940. G. R. SCOTT 2,195,097

Q METHOD OF MACHINING GLOBOIDAL WORM GEARS Filed May 12, 1957 2 Sheets-Sheet 1 INVENTOR 'earge 72", 56022 A TTORNE is.

March 26,1940.

G. R. sco'r'r 2,195,097 METHOD OF MACHINING GLOBOIDAL WORM GEARS I Filed May 12, 1957 zsheets-sheet 2 N V E N T O R George 5 6025.

BYY

. v H A TTOR NE V5.

Patented Mar. 26,

WORM GEARS 1 METHOD OF MACHINING GLOBQIDAL George B. Scott, Detroit, Mich.

" Application m 12, 1931, Serial No. 10,050

10 Claims.

My invention relates to methods and means for machiningworm gear elements and particularly to-a method and tool for accurately machining the flanks of the teeth of a worm or worm wheel 5 through the axial feeding of the tool as it is simultaneously rotated'substantially on the lead of the thread thereof.

When manufacturing worm gear sets of the enveloping type or double enveloping type, it is necessary to machine the thread of the worm and the teeth of the wheel in the central plane of the blanks. Finishing cuts must be taken when -on correct center relation on lines tangent to the theoretical base circle of the wheel. When 16 worm gear elements of the enveloping type are machined in this manner, surface engagement -is obtained between the threads of the worm and the engaged teeth of the wheel. Heretoi'ore, the machining was accomplished by a tool havin go teeth of narrower width than the gap to be ultimately formed between the thread and/or teeth of the worm gear element. A roughing operation occurred as the tool and blank were rotated in synchronism while their axes were advanced into :5 correct center relation. It is well known that the in movement of the cutting edges in this manner deforms the teeth sides so that they lack mating capacity. The tool was then rotated to advance the cutting edges sidewardly to widen the gaps by the machining which-occurred on correct center distances in the central plane of the blank. Correct forms were thereby produced on the'teeth flanks.

While the present invention applies to machining either element of a worm gear set, I will describe in detail the machining of a worm, gear with a half-hob or a plurality thereof, and make referencetothe use of one or a pair of cutters for employing a similar method of machining for accurately forming teeth in the worm wheel.

In practicing my present method for machining worm gears, I utilize a half hob mounted with its axis in correct center relation with a worm gear blank but shifted axially out of exact mating relation with the blank. Such a half hob may be mounted in a machine having a multiple feed. This is to say a feed in rotation and one (Cl. 90-3) v pose of illustration 8. half-hob as asleeve threaded on a shaft on a lead equal substantially to the 1 mean helical lead of the teeth. I provide means for shifting the half-hob axially on the shaft to produce its rotation as it is tangentially fed relative to the blank. After the half-hob is so fed to reach its center relation with the blank, the machining of one side of the thread may be completed or additional means may be provided to advance the half-hob in rotation, while operating in synchronism with the blank, to machine one side of the gaps originally formed in the blank to accurate form. v

A pair of half-hobs may be employed in this manner, one disposed above and the other below the blank to provide a balanced torque-condition. The half-hobs may be so adjusted that when they reach their mating relation with the blank one side of the teeth of the blank will be accurately machined by one half-hob while the opposite side of the teeth will be accurately machined by the other half-hob.

Similarly the pair of hobs may be mounted on the same shaft and advanced towardeach other during the time each is rotated on a lead substantially equal to the mean helical lead of the hob thread until they reach mated position where automatically the opposite'sides of the wheel teeth will be accurately machined.

Accordingly, the main objects of my invention are to machine the worm gear elements through the tangential advancement of a tool relativethereto during the time the tool is rotated in synchronlsm with the advancement of a lead substantially equal to the mean helical lead of the worm thread; to machine worm wheel teeth with a half-hob by tangentially advancing the halfhob until .in mated relation with the blank to rough out the teeth and thereafter, if necessary, to change the position of the hob in rotation to widen the gaps initially formed while machining accurate flanks on the teeth sides; to machine the teeth of a worm wheel by a pair of halfhobs which are mounted on opposite sides of the blank to provide a balanced torque condition and feeding the half-hobs tangentially in the same direction while rotated in synchronism substantially on the helical lead of the half-hob teeth; to have a pair of half-hobs so adjusted that after axial advancement into mating relation the teeth of one half-hobwill finish one side of the'teeth of the worm wheel while the teeth of the other half-hob will machine the opposite side of said' teeth; to mount two half-hobs for axial movement toward each other and machining the teeth i of a worm wheel blank through the movement of the hobs axially during the time they are rotated on a lead substantially equal to the mean lead of the half hob teeth; to provide means. for accurately adjusting the position of thehobs to have the tangential feeding thereof stopped when in accurate mating relation with the worm wheel blank; to have the teeth of one half hob machine one side of the worm wheel teeth while I the teeth of the other hob portion machines .theopposite sides of said teeth, and in general. to

provide means for accurately machining the teeth of worm gear elements which is positive in operation and economical of manufacture.

Other objects and features of novelty of my invention will be either specifically pointed out or will become apparent when referring, for a better understanding of my invention, to the following description taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a broken view, partly in section and P rtly in elevation of apparatus embodying features of my invention; 7 v Fig. 2 is a view of the structure illustrated in Fig. 1 after the tool has been moved into mating relation with a gear blank;

Fig. 3 is a view of the structure shown in Figs. 1 and 2 and disclosing thefurther turning movement applied to the tool to advance the cutting edges to widen the gap initially cut;

Fig. 4 is a sectional view of the structures'ib' lustrated in Fig. 8, taken on the line 4-4 thereof; Fig. 5'is a view of structure, similar to that of Fig. 1, showing a further form which my invention may assume; K

Fig. 6 is a view of structure, similar tothat of Fig. 5, showing a. further modified form of my invention, and

Fig. 'l is a broken view, in elevation. of cutting tools for machining a worm gear by method embodying my invention.

In Fig. 1, I have illustrated a worm wheel blank II, which is to be machined. 'A tool II in the nature of a half-hob is mounted in true center relation to the gear blank I. but disposed axiallyat one side of its mating position sufilcient to have the teeth out of engagement with the blank. The tool II is herein illustrated as a sleeve havmg a thread I! cut on the inside thereof which has a helix'angle which may be substantially equal to the mean helical lead of the teeth I! of the tool. The sleeve is mounted on 'a shaft M which is provided with a thread II engaging the thread l2 of the sleeve. The shaft id is journaled at one end in axbearing It and at the oppodte end in a bearing". -The housing It.

carrying the bearing-IS, alsosupport's a'lead' screw. ll which regulates the position of a collar.

II which .is slidable longitudinally of the shaft Id. The lead screw-l0 is operated by a hand wheel 22. v

The opposite end of'th'e'shaft gear 23 keyed thereto and driven by a worm 2.4

-which-is mountedon a shaft II. Theshaft ll is provided with a pair of spaced collars a in which isnested abifurcated IIcarrie'd on a rod 20. The rod II is mounted for longitudinal move-. ment and employed for shifting the shaft 2! to move the worm ll longitudinally to thereby provide an increment of rotation to the shaft N,

'Ihe shaft II is driven in with the spindle of thege'arblank ll (not shown) to provide the synchronised operation of the tool ll and the blank ll.

During theoperation the hand wheeltfmay arcane? roughed out and if properly adjusted, one side of the teeth is finished. 7 As pointed out hereinabove, the end feeding of the tool teeth into a blank of the enveloping type will produce deformed teeth thereon and for this reason the teeth I I of. the

half-hob are of narrower width than the gap to be ultimately formed between the teeth 28 of the blank. I

After-the tool and blank have been disposed in mating relation on true center distances, when not adjusted to'finish a side of the teeth, the

rod fl may be shifted a predetermined amount to move the worm 24 longitudinally as illustrated in Fig. 3. An additional movement in rotation is thereby imparted to the toolll, resulting in the advancement of the lead of the teeth II of the half-hob relative to the teeth 29 of the blank. As a result, the gaps between the teeth are widened by machining one side of the blank teeth inthe central plane of the blank when the tool and blank are in exact mated tion. The arbor of the tool or blank may then be shifted end for end and a'machine opposition performed on the other side of the blank teeth to have both ends accurately spaced and formed.

In Fig. 4, I have illustrated the machining of the teeth I! of the blank after the tool has been moved-into exact mating relation therewith, to illustrate the widening of the gap due to the shifting of the teeth due to the rotation of the tool and the machining on the central plane of the blank with the cutting edges disp sed on a tangent to its theoretical base circle.

In Fig. 5, I have shown a further form which my invention may assume. In this instance a pair of half-hobs ii are employed which are similar to the half-hob ll illustrated and described with reference as Figs. 1 to 4. inclusive. The half-hobs ii are mounted on diametrically opposite sides of a spindle 32 of the gear blank II and are driven in opposite directions. The half-hobs II are fed longitudinally of the blank while their axes are maintained in true center relation until they reach mating position. The

half-hobs'll are so adjusted that theteeth of one half-hob cut-the flanks of one sideof the teethoftheblankwhilethe teeth ofthe other half-hob cut the flanks of the opposite side of mentisiequiredwhmadjmtmentismadeto widenthegapsthroughth'eoperationofthe half-hobswhendispo'sedin'exaet mating posi- 'theteeth. Abalancedtorqueconditionresuitsdfl whichisdesirableandnoadditionalfeedmova. llhasawormtion. While I-have illustrated the half-hobs .3! t5 asbeingaleeveshaving'threads il'mountedthereinwhiehengag'ethethreads llon theshaft u, it is to be that ainachine having a differential movement may be employed for in accordance with the meanleadof'thethreadliinadditiontothesynchroniaedrotationofthetoolandblank. Such differential movement'advanc'es thehobintotrue moving thehaif-hobs longitudinallyas they-are l0 mating'reiationwiththegearblank. ltistobe'll 6 made to effect the finishing operation asdescribed with reference to the half-hob illustrated in Fig. 4.

In Fig. 6, I have shown a further form which my invention may assume. In this instance, a

10 pair of half-hobs M are disposed on a single shaft 42. The half-hobs and the blank ll are driven in synchronism while the half-hobs are advanced toward each other and rotated substantially on the mean lead of the thread of the half-hob teeth. The teeth I! of the half-hobs will rough out the gaps between the teeth 2! of the blank during their synchronized movement toward each other and when reaching mating position with the blank will widen the gaps by 80 having the teeth of one of the half-hobs cut away material on one side of the teeth 29 of the blanks while the teeth on the other half-hob will machine the opposite sides of-said teeth. While a machine having differential movements 15 may be employed for moving the half-hobs ll towards each other into mating position, I have illustrated arms 43 which may be adjusted'toward each other for effecting longitudinal movement which in turn produces synchronized ro- 80 tation of the half-hobs ll through the engagement of the teeth I! u'pon the shaft 42 with the thread I! of the half-hobs ll. When the infeeding of the hobs into mating relation produces only a roughing operation it is to be understood that the teeth may be 'advainttiled preferably by a turning movement as set to above, to produce aflnishing operation on the sides of the teeth.

In any instance, the'machining. of the teeth 20 of the blank occurs through the mounting to 'of the tool on a shaft disposed-in true center relation with the spindle of the blank but with the tool axially out of shifted mating relation. The roughing of the teeth occurs through the longitudinal movement of the toolv toward mated 6 position synchronized, with an increment of rotation substantially on the mean lead of the hob teeth. After the hob has reached matin position it may be shifted in rotation to advance the cutting edges laterally to machine the flanks 80 of the teeth toproduce accurate tooth forms.

When a single half-hob is employed the arbor of the blank or tool may be shifted end for end to machine the opposite side of the teeth'ilanks. When two of the half-hobs are employed they 56 may be adjusted to automatically widen the gaps in the blank when they reach their mating position. One of the-hobs will machine one side of the teeth while the other hob will machine the opposite sides of the teeth. The hobs may be do vdisposed on the same shaft and move toward each other or be mounted on separate shafts and positioned diametrically opposite each other .with reference to the blank to provide a baianced torque condition with relation to the blank 65 arbor.

In Fig. 'l I have illustrated a pair of cutting tools SI in position to operate toaccurately machine a worm blank 52. This illustration was made to show how the principles explained in I0 detail hereinabove. for machining worm wheels with half-hobs may be employed for machining worm gears when utilizing one or a plurality of I worm gear cutters. Thecutters II and I per se, may be of any well known type. but a'rs ref- 7 erabiysimilartothosedescribedandclaimedin my co-pending application, Serial No. 735,975, filed July 19, 1934, for Cutting tool.

The example illustrated embodies the mounting of the pair of cutters and Si on a shaft 53 with the shanks 54 of the tools having an internal thread which engages threads 55 and 56' of the shaft. The threads are disposed substantially on the helix of the thread of the worm gear and effect the turning of the cutters in synchronism with their advancement during the time the cutters and wormgears are rotated in synchronism. When the cutters have advanced into the midplane of the worm the cutting edges on one side of the teeth of one cutter accurately machine one side of the grooves while the cutting edges of the other cutter 'flnish the opposite side of the grooves. It is to be understood that a single cutter may be employed to be advanced along the axis of its arbor into the central plane of the worm gear and thereby accurately finish one side of the gap thereof, the opposite side of which-may be finished through the shifting of the axis ofthe tool or-wormgear end for end.

It is alsowithin the purview of my invention to dispose a cutter on opposite sides of the worm to provide a balanced torque condition with relation to the worm. gear axis and move the tools axially into'the plane of the worm gearand finish opposite sides of the gaps when in the said plane. It is to beunderstood that an additional increment of rotation may be provided to the cutters or worm gear to relatively advance the cuttingedges laterally when disposed in the plane through the axis of the worm gear to eifect .a

-. finishing operation to widen the initially formed gapsto a predetermined dimension.

While I have described and illustrated several embodiments ofrmy invention, it will be apparent to those skilled in the art that various changes, omissions, additions \and substitutions may be made therein withoutideparting from the spirit and scope of my invention as set forth in the accompanying claims. I I What I claim is: a

l. The method of machining a worm gear element of the enveloping type wherein a tool with mating teeth will deform teeth being machined which includes the steps; of mounting the tool havingteethof less width than said mating teeth and blank on 'correct axis relation with the tool shifted from correct mated position, of driving the tool and blank in synchronism; of axially shifting the tool into mated position with the blank while the tool and blank are operating in synchronism, of imparting an additional movement in rotation to the toolin synchronism with said axial advancement, of accurately stopping said advancement at mated position to accurately machine one side of said gap without further adjustment, and of imparting a still further increment of movement in reverse rotation to said tool to machine the other side of said gap. I

2. The method of machining a worm gear element of the enveloping type wherein a tool with mating teeth will deform teeth being machined which includes the steps; of mounting the tool having teeth of less width than said mating teeth and blank on correct axis relation with the tool shifted from correct mated position; of driving the tool and blank-in synchronism; of axially shifting-the tool into mated position with the blank while operating in synchronism; of imparting a movement in rotation to the'tooi in synchronism with said axial advancement; and of imparting an additional movement in rotation to the teeth of the tool when m mated relation with the blank to finish the sides of the blank 3. The method of machining a worm gear element of the enveloping type wherein a tool with mating teeth will deform teeth being machined which includes the steps; of mounting the tool having teeth of less width than said mating teeth the tool and blank in synchronism; of axially shifting the tool into mated position with the blank while operating in synchronism; of imparting a movement in rotation to the tool synchronized with the axial movement to have the teeth of the'tool advanced substantially on the lead of the thread thereof; and of imparting an additional movement in rotation to the tool after its axial advancement into mated position to advance the tool teeth to finish machining the sides of the blank teeth.

4. The method of machining a worm wheel of the enveloping type wherein a tool with mating teeth will deform teeth being machined which includes the steps; of mating a half-hob oi the enveloping type having teeth less thickness than said mating teeth and blank on correct axis relation with the half-hob shifted axially from than said mating teeth and blank on correct axis relation with the half-hob shifted axially from correct mated position; of operating the half-hob and blank insynchronism; of advancing the halfhob axially into mating position as it is rotated in synchronism with such advancement substantially on the lead of the hob teeth; and of imparting a movement in rotation to the half-hob after it has reached mating position to advance the cutting edge of the teeth into the sides of the teeth of the blank.

6. The method of machining a worm gear element which includes the steps; of mounting a pairjof tools on diametrically oppoflte sides of a blank with their axes in correct center relation but shifted axially out of mating, position; of

shifting said tools in the same direction while rotating them. in the opposite direction -in synchronism to have the advancement occur on the lead of-the helical teeth; and stoppin said advancement when, the tools reach exact mating relation with the teeth of one tool finishing the teeth of one side of the blank, while those of the 2:15; tool are finishing the opposite side of said 'LThemethcdofmachining aworm wheel which includes the steps; of maintaining a'pair of half-hobs on diametrically opposite sides of the wheel blank with their'axes in correct center relation, but shiftedaxially out of mating position; of shifting said half-hobs in the same di-' rection while rotating them in the oppositedirectionin synchronism to have the advancement occur substantially on the lead of the half-hob teeth, and stopping said advancement when the half-hobs reach exact mating relation with the teeth of one half-hob finishing the teeth on one side of the blank while those of the other half-hob are finishing the opposite side of said teeth.

8, The method of machining a worm wheel which includesthe steps; of mounting a pair of half-hobs on a shaft which'is in correct center relation with the shaft of the blank with the halfhobs spaced from each other out of mating relation with said blank; of shifting said half-hobs toward each other while rotating them in the opposite direction in synehronlsm to have the advancement occur substantially on the lead of the half-hob teeth; and stopping said advancement when the half-hobs reach exact mating relation with the teeth of one half-hob finishing the teeth on one side of the blank while those of the other half-hob are finishing the opposite side of said teeth. r

9. The method of machining a worm wheel of the enveloping p which includes, mating a halfxhob of the enveloping type with a worm A wheel blank with the axis of said hob in proper tangential position with respect to said blank, rotating said hob and blank in synchronism, moving said hob axially and at the same time rotating said hob along a lead substantially equal to the lead of the hob teeth, and'subsequently imparting a rotational movement to said hob to advance the cutting edges of the teeth into the sides of the teeth of the worm blank.

10. The method of machining a worm wheel which includes the steps of maintaining a pair of half hobs on proper axes with respect to the axisofawormwheelblanktobemachinedbut with said hobs shifted axially out of mating position, of shifting said ball hobs along their axes in a direction generally tangential to the worm wheel blank to be finished while rotating them alongaleadequaltotheleadoftheteethof' said ball hobs, discontinuing the axial advancement of said half hobs when the same have reached exact matingrelation with the worm wheel and rotating said hobs one in one direction and onein the opposite direction relatively to GEORGE R. 'sco'rrr 

